Direct Visualization of Quantum Scars in a Stadium Shaped Graphene Quantum Dot
The study of quantum classical correspondence can not only provide fundamental insights into the connections between classical and quantum mechanics, but also help achieve intuitive understandings of quantum phenomena. Among various systems studied before, the quantum classical correspondence in quantum systems with corresponding classical chaotic dynamics is of special interest. One reason is that the required non-linearity for classical chaos (exponential sensitivity to initial conditions) is absent in quantum mechanics, so it is of fundamental interest to understand in what form classical chaos will be manifested in quantum systems. Quantum scar, which refers to wavefunctions with enhanced probability density in the vicinity of unstable classical periodic orbits, is one example demonstration of the quantum classical correspondence in classically chaotic quantum systems. Since its first prediction almost 40 years ago, the direct visualization of quantum scars in real quantum systems is still elusive. Yet, the experimental verification of many new types of quantum scars proposed in recent years, such as relativistic quantum scars, perturbation induced quantum scars, and chiral quantum scars, demands experimental techniques that can directly visualize quantum scars with both high spatial and high energy resolutions. In this talk, I will show our recent experimental results on the in-situ creation and wavefunction mapping of stadium shaped graphene quantum dots by using a low temperature scanning tunneling microscope in attempting to achieve the direct visualization of quantum scars.
Zhehao Ge is a postdoctoral researcher in Michael Crommie’s group in the physics department at UC Berkeley. His current research focuses on STM/STS study of novel devices and nanostructures based on Van der Waals 2D materials. Zhehao obtained his PhD degree from UC Santa Cruz in July 2023, his PhD research focused on STM/STS measurement of in-situ created graphene quantum dots.
Engineering Small HOMO-LUMO Gap 0D molecules Using 1D Topology Principles
Previous studies have shown that integrating heterojunctions into 7-AGNR and 9-AGNR scaffolds can create topologically protected states. These states, when built into 1-dimensional graphene nanoribbons have been shown to create topological insulators with new states between the bulk states of the ribbon. This is due to the unique topology of the specifically chosen 7-AGNR and 9-AGNR unit cells. The topological phases of a graphene nanoribbon are affected by the edge structure, width, and unit cell of the GNR, all of which define the ℤ2 invariant. Singly occupied states were shown to occur where a fused topologically trivial (ℤ2 = 0) and topologically nontrivial (ℤ2 = 1) GNR segment meet.
This same principle can be used to synthesize small molecules as well. However, since the molecule has discrete ends close to the topological heterojunctions extra care is required to ensure that there is not an additional topological end-state that couples with the heterojunction and quenches the in-gap states. In this talk I will discuss our work in the synthesis of small HOMO LUMO gap molecules as well as their characterization by scanning tunneling microscopy and spectroscopy. We have found that by utilizing these design principles we are able to access wholly organic single molecules with HOMO LUMO gaps of approximately 150 meV, a range that is commonly only associated with inorganic semiconductors.
Kaitlin Slicker is a 5th year synthetic graduate student in Dr. Felix Fischer’s group where she works on the synthesis of graphene nanoribbon monomer precursors. She obtained her undergraduate degrees at the Georgia Institute of Technology in biology and chemistry in 2019 where she worked for Dr. Seth Marder synthesizing materials for organic electronics. In her free time, she enjoys hiking, biking, baking, and eating at Chick-fil-A.